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IB BIOLOGY 2.3 EUKARYOTIC CELLS 2.3.1 Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell http://www.youtube.com/watch?v=NiiLS_ovLwM&feature=related video on eukaryotic cell. 2.3.2 Annotate the diagram from 2.3.1 with the functions of each named structure Organelles of eukaryotic cells Common organelles include the following Endoplasmic reticulum Ribosomes Lysosomes ( not usually in plant cells) Golgi apparatus Mitochondria Nucleus Chloroplasts Centrosomes Vacuoles Cytoplasm All eukaryotic cells have a region called the cytoplasm that occurs inside the plasma membrane or the outer boundary of the cell. It is in this region that the organelles occur. Endoplasmic reticulum The endoplasmic reticulum (ER) is an extensive network of tubules or channels that extends almost everywhere in the cell from the nucleus to the plasma membrane. The ER is of two types: smooth and rough. Smooth ER does not have any of the organelles called ribosomes on its exterior surface. Rough ER has ribosomes attached to it. Functions of RER Helps in the synthesis of proteins. Functions of SER Production of membrane phospholipids and cellular lipids Production of sex hormones such as testosterone and estrogen Detoxification of drugs in the liver Storage of calcium ions needed for contraction in muscle fibres. Transportation of lipid based compounds. To aid the liver in releasing glucose into the bloodstream when needed. Ribosomes Ribosomes carry out protein synthesis in the cell. These structures may be found free in the cytoplasm or maybe attached to the surface of the endoplasmic reticulum. They are always composed of a type of RNA and protein. Lysosomes Lysosomes are intracellular digestive centres that arise from the Golgi apparatus. The lysosomes lack any internal structures. They are sacs bounded by a membrane that contains as many as 40 different enzymes. These enzymes are hydrolytic and catalyze the breakdown of proteins, nucleic acids, lipids and carbohydrates. Functions: Lysosomes fuse with the old or damaged organelles from within the cell to break down so that recycling of the components occur. Lysossomes are also involved with the breakdown of materials that are brought into the cell by phagocytosis. The interior of a functioning lyssome is acidic which is suitable for the enzymes to hydrolyse large molecules. The newly formed lysosome is called the primary lysosome and when it fuses with the food vacuole it is called the secondary lysosome. Golgi apparatus. The Golgi apparatus consists of flattened sacs called cisternae which are stacked upon one another . Functions This organelle functions in collection, packaging, modification, and distribution of materials synthesized in the cell. The side of the apparatus near ER is called the cis side. It receives products from ER. These products move into the cisternae of the Golgi apparatus. Movement then continues to the discharging or opposite side, the trans side. Small sacs called the vesicles can be seen coming off the trans side. These vesicles carry modified materials to wherever they are needed inside or outside the cell. This organelle is prevalent especially in glandular cells such as those in the pancreas, which manufacture and secrete substances. Mitochondria Mitochondria are organelles that carry out cellular respiration in nearly all eukaryotic cells, converting the chemical energy of foods such as sugars to the chemical energy of a molecule called ATP( Adenosine triphosphate). Because of this the mitochondrion is often called the “cell powerhouse” Mitochondria are rod shaped organelles that appear throughout the cytoplasm. They have their own DNA. It also produces and contains its own ribosomes. They have a double membrane. The outer membrane is smooth, but the inner membrane is folded into cristae. Inside the inner membrane is a semi-fluid substance called matrix. An area called inner membrane space lies between the two membranes. The cristae provide a huge surface area for the chemical reactions (cellular respiration) to occur. Cells that have high energy requirements, such as the muscle cells, have large number of mitochondria. . An area called inner membrane space lies between the two membranes. The cristae provide a huge surface area for the chemical reactions (cellular respiration) to occur. Cells that have high energy requirements, such as the muscle cells, have large number of mitochondria. Mitochondria are organelles that carry out cellular respiration in nearly all eukaryotic cells, converting the chemical energy of foods such as sugars to the chemical energy of a molecule called ATP( Adenosine triphosphate). Because of this the mitochondrion is often called the “cell powerhouse” Mitochondria are rod shaped organelles that appear throughout the cytoplasm. They have their own DNA. It also produces and contains its own ribosomes. They have a double membrane. The outer membrane is smooth, but the inner membrane is folded into cristae. Inside the inner membrane is a semi-fluid substance called matrix. An area called inner membrane space lies between the two membranes. The cristae provide a huge surface area for the chemical reactions (cellular respiration) to occur. Cells that have high energy requirements, such as the muscle cells, have large number of mitochondria. Electron micrograph of mitochondria. Nucleus Nucleus is bounded by a double membrane referred to as the nuclear envelope. This membrane allows compartmentalization of the eukaryotic DNA, thus providing an area where DNA can carry out its functions and not be affected by processes occurring in other parts of the cell. The nuclear membrane does not provide complete isolation as it has numerous pores that allow communication with the cell’s cytoplasm/ The DNA of eukaryotic cells often occurs in the form of chromosomes. Chromosomes vary in number depending upon the species. Chromosomes carry all the information necessary for the cell to exist. DNA is the genetic material of the cell. It enables certain traits to be passed to the next generation. When the cell is not in the dividing process, the chromosomes are not present as visible structures. The DNA is in the form of chromatin. Chromatin is formed of strands of DNA and proteins called histones. Within the nucleus is nucleolus. Function Molecules of the cell ribosomes are manufactured in the nucleolus. Chloroplast CHLOROPLAST: Chloroplasts occur in plant cells. The chloroplast contains a double membrane. The space enclosed by the inner membrane, contains a thick fluid called stroma . The chloroplast contains its own DNA and 70S ribosomes. The interior of the chloroplast includes the grana, the thylakoids, and the stroma. The granum is composed of numerous thylakoids stacked like a pile of coins. The thylakoids are flattened sacs with components necessary for the absorption of light. Stroma contains many enzymes and chemicals necessary to complete the process of photosynthesis. Chloroplasts are capable of reproducing independently of the cell. Function: Involved in the process of photosynthesis and helps in the conversion of light energy to chemical energy stored in sugar molecules. Centrosome: It occurs in all eukaryotic cells. It consists of a pair of centrioles at right angles to one another. Higher plant cells produce microtubules even though they do not have centrioles. The centrosome is located at one end of the cell close to the nucleus. Functions These centrioles are involved in assembling microtubules which are important to the cell in providing structure and allowing movement. Microtubules are important to cell division. Vacuoles Vacuoles are large storage organelles that usually form from the Golgi apparatus. They are membrane bound organelles and occupy a very large space inside the cells of most plants. Functions They store a number of different substances including potential food, metabolic wastes and toxins to be expelled from the cell, and water. Vacuoles enable cells to have higher surface are to volume ratios even at larger sizes. In plants they allow an uptake of water that provides rigidity for the organism. 2.3.3. Identify structures from 2.3.1 in electron micrographs of liver cell Electron micrograph of a liver cell Look at electron micrographs in the internet to understand labeling. 2.3.4 Compare prokaryotic and eukaryotic cells Feature Type of genetic material Prokarytoic cells A naked loop of DNA/ DNA in a ring form without protein Eukaryotic cells Chromosomes consisting of strands of DNA associated Location of genetic material In the cytoplasm in a region called the nucleoid/ DNA free in the cytoplasm Mitochondria Ribosomes Internal membranes No mitochondria Small sized- 70S Few or none are present Size 0.5 – 1.0 micrometers with protein. In the nucleus inside a double nuclear membrane called the nuclear envelope/DNA enclosed within a nuclear envelope Always present Larger sized -80S Many internal membranes that compartmentalize the cytoplasm including ER, Golgi apparatus, lysosomes Size more than 10 micrometers. 2.3.5 State three differences between plant and animal cells. Feature Cell wall Chloroplast Vacuole Plant cells Cell wall and plasma membrane are present. Chloroplasts are present in the cytoplasm. Large fluid-filled vacuole often present Animal cells No cell wall, only a plasma membrane is present. There are no chloroplasts Not usually present polysaccharide Shape Centriole Store carbohydrate as starch. Fixed shape, usually rather regular. Do not contain centriole within a centrosome area Store carbohydrate as glycogen. Able to change shape. Usually rather regular. Contain centriole within a centrosome area. 2.3.6 Outline two roles of extracellular components Extracellular components and their functions: The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity. Cell wall protects the plants and provide the skeletal support that keep plants upright on land. It consists of fibres of polysaccharide cellulose embedded in a matrix of other polysaccharides and proteins. Because of its rigidity, it only allows only a certain amount of water to enter the cell. In plants, when adequate amount of water is inside the cell, there is pressure against the cell wall. That pressure helps to support the plant’s upright position. Cell Bacteria Fungi Yeasts Algae Plants Animals Outermost part Cell wall of peptidoglycan Cell wall of chitin Cell wall of glucan and mannan Cell wall of cellulose Cell wall of cellulose No cell wall; plasma membrane secretes a mixture of sugar and proteins called glycoproteins that forms the extracellular matrix. Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement. This layer helps hold cells together in tissues and can have protective and supportive functions. The extracellular matrix (ECM) of many animal cells is composed of collagen fibres plus a combination of sugars and proteins called glycoporteins. These form fibre-like structure that anchor the matrix to the plasma membrane. This strengthens the plasma membrane and allows attachment between adjacent cells. The ECM allows for cell-to-cell interaction, and bringing about coordination of cell action within the tissue. ADDITIONAL INFORMATION CYTOSKELETON: Eukaryotic cells contain a network of protein fibers, collectively called the cytoskeleton, extending throughout the cytoplasm. Functions: they provide structural support, and are involved in various types of cell movement. Three main types of fiber make up the cytoskeleton: Microfilament(the thinnest type of fiber) Microtubules ( the thickest type pf fiber) And Intermediate filaments. Microfilaments, also called actin flilaments. It is made of globular protein called actin. Present inside the plasma membrane and helps support cell’s shape. It interacts with other kinds of protein filaments to make cells contract. Intermediate filaments are made of fibrous proteins and have a rope like structure. Function: reinforcing cell shape and anchoring certain organelles, for example nucleus is held in place with the help of intermediate filaments. Microtubules are straight hollow tubes composed of globular proteins called tubulin. Functions: Provide rigidity and shape. Provide anchorage for organelles and to act as tracks for organelle movement within the cytoplasm. Lysosomes might move along a microtubule to reach a food vacuole. Guide the movement of chromosomes when cells divide CILIA AND FLAGELLA: Cilia are short and numerous appendages that helps in movement in organisms such as Paramecium. Flagella are longer, generally less numerous appendages seen in protists such as Euglena Cilia lining the upper respiratory tract in multicellular organisms. Flagellum on a sperm cell. Both flagella and cilia are composed of microtubules wrapped in an extension of the plasma membrane. A ring of nine microtubules doublets surrounds a central pair of microtubules. This arrangement seen in cilia and flagella is called 9+2 pattern. The anchoring structure is called a basal body. Bending movement of cilia/flagella involves protein called dynein arms that are attached to each microtubule doublet. Dynein arms are powered by ATP, move neighbouring doublets of microtubules relative to one another. Because they are anchored within the organelle, the doublets bend instead of sliding past one another. CELL WALL: Cell wall protects the cells in plants and provide the skeletal support that keeps plants upright on land. Plant cell wall consists of fibers of the polysaccharide cellulose embedded in a matrix of other polysaccharides and proteins. Cell walls are multilayered. Between the walls of adjacent cells is a layer of sticky polysaccharide that glues the cells together. Cell walls of certain plants are made of lignin. Plasmodesmata channels between adjacent plant cells. It forms a communicating system connecting the cells in plant tissues. Plasma membrane and the cytoplasmic fluid of the cells extend through the plasmodesmata, so that water and other molecules can readily pass from cell to cell. It helps the cells of the plants to share water, nourishment and chemical messages. Animal cells do not have cell wall but most of them secrete a sticky layer of glycoprotein called the extracellular matrix. These form fibre-like structures that anchor the matrix to the plasma membrane. This strengthens the plasma membrane and allows attachment between adjacent cells. Researchers have discovered that ECM helps regulate cell behavior, probably through contact with proteins in the plasma membrane. Adjacent cells in many animal tissues also connect by cell junctions. There are three general types. Tight junction: Binds cells together, forming a leak proof sheet. It is seen lining the digestive tract, preventing the contents from leaking into the surrounding tissues. Anchoring junctions: Rivet cells together with cytoskeletal fibers, forming strong sheets. Seen in skin and heart muscle.(stretching and mechanical stress ) Gap junctions: They allow small molecules to flow between neighboring cells. For example, flow of ions through gap junctions in the cells of heart muscle coordinates their contraction.